Microsoft on Monday promised that Office 365 ProPlus subscribers would have access to OneDrive for Business, the company's enterprise-grade cloud storage service, by the end of January 2015.

Initially, OneDrive for Business will come with a 1TB-per-user maximum. But as Microsoft rolls out unlimited storage to other Office 365 plans' subscribers, those with Office 365 ProPlus will also receive the infinite allowance.

Office 365 ProPlus is a $12-per-user-per-month subscription that provides business workers with rights to Office 2013 on Windows and Office for Mac 2011, as well as rights to Office for iPad and commercial use of the iPhone and Android Office apps.

Unlike most other Office 365 rent-not-buy plans, ProPlus does not come with off-premises Exchange and Lync; the latter, Microsoft's chat, video calling and telephony service, is to be renamed Skype for Business in 2015.

Office 365 ProPlus is instead a substitute for traditionally-licensed Office 2013 and Office for Mac 2011, and usually adopted by companies that still prefer to run their Microsoft backend servers -- Exchange, in particular -- on premises.

The addition of OneDrive to Office 365 ProPlus will be another way for Microsoft to pitch such partial subscriptions to firms that are reluctant or unable to go all-in on the cloud.

In an interview earlier this month about Microsoft's decision to give editing rights to consumers using Office for iPad, Wes Miller, an analyst with Directions on Microsoft, pointed out that Office 365 ProPlus is gaining ground in the enterprise.

"Using Office 365 ProPlus has been in the conversations considerably more when we do our licensing boot camps," said Miller, referring to the two-day workshops the research firm hosts to help companies understand the obscure and confusing rules of Microsoft's software licensing. "They're looking at going to Office 365 ProPlus for the desktop side."

When Microsoft bumped up the storage space for OneDrive for Business to 1TB in April, it said it would add the cloud-based service to Office 365 ProPlus, but did not provide a timeline. In October, it said that after Dec. 1, all new ProPlus subscriptions would receive OneDrive for Business. At the same time, it acknowledged problems extending the service to existing customers.

"We have had some delays with the service rollout for existing Office 365 ProPlus customers -- we're working on a solution and will share more specifics soon," Microsoft said in an updated blog post.

Today, Microsoft said that it would start the Office for Business rollout to existing ProPlus subscribers before year's end, and finish before the end of January 2015.

Microsoft has not given a timetable for boosting the 1TB limit of OneDrive for Business to unlimited, but has said it will do so in 2015 for customers who have signed up for the "First Release" enterprise preview program.

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